1. Field of the Invention
The present invention relates to a rotary head apparatus including at least one magnetic head and a magnetic playback apparatus using the same, and more particularly, the present invention relates to a rotary head which includes at least one magnetic head, with which a recording medium is unlikely scraped, and which prevents a decrease in output and deterioration in an error-detection characteristic due to a spacing loss caused by a deposition produced when the recording medium is scraped, and also relates to a magnetic playback apparatus using the same.
2. Description of the Related Art
In some of magnetic recording and playback apparatuses for use in video equipment or for saving computer data, a rotary head apparatus includes a rotary drum having at least one magnetic head mounted thereon, and when a magnetic tape runs while keeping in contact with the rotary drum along a helical trajectory, and the rotary drum rotates, data is recorded into and played back from the magnetic tape by the helical scanning method.
FIG. 8 is a plan view of a rotary head apparatus having magnetic heads mounted thereon and disposed in a magnetic recording and playback apparatus. FIG. 9 is a perspective view of an example magnetic head mounted on the rotary head apparatus. FIG. 10A is a plan view of the magnetic head shown in FIG. 9, and viewed from the Z1 direction indicated in FIG. 9 and rotated clockwise by 90 degrees, and FIGS. 10B to 10D are illustrations respectively taken along the lines XB—XB, XC—XC, and XD—XD and viewed from the arrow X indicated in FIG. 10A. FIG. 11 is a partially magnified view illustrating a state in which a magnetic tape lies in contact with the rotary head apparatus shown in FIG. 8. FIG. 12 is a plan view of the magnetic head shown in FIG. 9 and viewed from the Y2 direction indicated in FIG. 9.
In a rotary head apparatus 1 shown in FIG. 8, a stationery drum (not shown) is fixed, and a rotary drum 1a is rotatably supported on the stationery drum so as to be coaxial therewith and is driven to rotate by a motor power in an upper-arrow direction indicated in the figure. A magnetic tape T serving as a recording medium is wound around the rotary head apparatus 1 by a predetermined angle along a helical trajectory and runs in a lower-arrow direction indicated in the figure. All the while, the rotary drum 1a rotates, and magnetic heads H1a and H1b mounted on the rotary drum 1a scan the magnetic tape T. In the rotary head apparatus 1, a couple of the magnetic playback heads H1a and H1b are disposed so as to face each other.
The magnetic head H1a shown in FIG. 9 is formed by a base member 2 composed of an alumina titanium carbide; a playback-use, magnetic-resonance-type (MR-type) thin-film magnetic head 3; an insulating layer 4 serving as a protecting layer, both formed by a thin film forming process; and a protecting base member 5 composed of an alumina titanium carbide and bonded on the insulating layer 4 by adhering means (not shown) such as an epoxy adhesive.
A magnetic gap 6 of the MR-type thin-film magnetic head 3 is exposed to a magnetic-tape opposing surface (surface facing toward Y2 in the figure) H1aA of the magnetic head H1a. The MR-type thin-film magnetic head 3 is supplied with current through electrodes 7.
The magnetic head H1a mounted on the rotary drum 1a abuts against the magnetic tape T in a state shown in FIG. 11. Meanwhile, the X1 and X2 directions in FIG. 11 indicate the rotating direction of the rotary drum 1a and the longitudinal direction serving as the sliding direction of the magnetic tape T, respectively.
As shown in FIG. 10A, the magnetic head H1a is shaped in a convex arc having a radius of curvature R, along the longitudinal direction serving as the sliding direction of the magnetic tape T. Also, as shown in FIG. 10B, the magnetic head H1a is shaped in a convex arc having a radius of curvature r, along the lateral direction (Z1-Z2 direction indicated in FIG. 9) perpendicular to the sliding direction of the magnetic tape T.
Since the recoding and playback apparatus is of a so-called helical scanning type, as shown in FIG. 12, the magnetic gap 6 of the MR-type thin-film magnetic head 3 disposed in the magnetic head H1a is slanted at an azimuth having an angle θ corresponding to the helical trajectory.
Right and left edges 8 and 9 of the tape-opposing surface H1aA are also slanted at the same angle as that of the azimuth of the magnetic gap 6. An acute angular corner 12 formed by the right edge 8 and an upper edge 10 lies further outwards in the longitudinal direction than a corner 13 formed by the right edge 8 and a lower edge 11, and a corner 14 formed by the left edge 9 and the upper edge 10 lies further inwards in the longitudinal direction than an acute angular corner 15 formed by the left edge 9 and the lower edge 11. Thus, the plane figure of the opposing surface H1aA viewed from the magnetic tape (from the Y2 side in FIG. 9) is a parallelogram as shown in FIG. 12.
The magnetic head H1b has the same structure as that of the magnetic head H1a. However, since the magnetic head H1b is provided with an azimuth in the opposite direction to the magnetic head H1a, the plane figure of an opposing surface H1bA of the magnetic head H1b viewed from the magnetic tape is a parallelogram slanted in the opposite direction to the magnetic head H1a. 
A hatched area in FIG. 12 indicates a magnetic-tape sliding area of the opposing surface H1aA in a state in which the magnetic head H1a is mounted on the rotary drum 1a and the magnetic tape slides on the opposing surface H1aA. The X1 direction in FIG. 12 indicates the longitudinal direction serving as the sliding direction of the magnetic tape T.
Japanese Unexamined Utility Model Application Publication No. 62-018812 has disclosed a magnetic head shaped in two convex arcs, one having the curvature of radius R along the sliding direction of a magnetic, and the other having the curvature of radius r along a direction perpendicular to the sliding direction.
As mentioned previously, the magnetic head H1a is formed such that the plane figure of the opposing surface H1aA viewed from the magnetic tape is a parallelogram. Accordingly, when the opposing surface H1aA is shaped in a convex arc having the curvature of radius r along the lateral direction, the apex of the convex arc having the curvature of radius r is likely formed toward the acute angular corners 12 and 15; as a result, a continuous line PL1 formed by the apex becomes a curve extending towards the acute angular corners 12 and 15, as shown by a dotted line in FIG. 12.
That is, in an area from the magnetic gap 6 to the right edge 8, as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner 12, the apex is displaced further away from the center line O—O laterally dividing the opposing surface H1aA into two parts, towards the upper edge 10, and, on the right edge 8, the apex is formed at substantially the same position as the acute angular corner 12.
For example, as shown in FIG. 10B, in the illustration taken along the center line XB—XB longitudinally dividing the magnetic head H1a into two parts and viewed from the X direction, the apex P1 lies on substantially the same line as the center line XB—XB. Also, as shown in FIG. 10C, in the illustration taken along the line XC—XC lying closer to the right edge 8 than the center line XB—XB and viewed from the X direction, the apex P2 lies at a position displaced away from the center line O—O towards the upper edge 10.
Meanwhile, in an area from the magnetic gap 6 to the left edge 9, as the apex of the convex arc having the curvature of radius r comes closer to the acute angular corner 15, the apex is displaced further away from the center line O—O towards the lower edge 11, and, on the left edge 19, the apex is formed at substantially the same position as the acute angular corner 15.
For example, as shown in FIG. 10D, in the illustration taken along the line XD—XD lying closer to the left edge 9 than the center line XB—XB and viewed from the X direction, the apex P3 lies at a position displaced away from the center line O—O towards the lower edge 11.
Meanwhile, since the magnetic head H1b is provided with an azimuth in an opposite direction to the magnetic head H1a, the displacement of the continuous line PL1 away from the center line O—O is symmetrical to the magnetic head H1a with respect to the center line O—O.
Accordingly, when the magnetic tape T comes into contact with and slides on the magnetic-tape sliding area of the opposing surface H1aA, in two areas L1 where the continuous line PL1 is displaced away from the center line O—O, the continuous line PL1 abuts against the magnetic tape T while having an angle generated in accordance with the displacement away from the center line O—O, thereby causing the continuous line PL1 to generate a sliding resistance against the magnetic tape T and resultantly scraping magnetic powder applied on the magnetic tape T. The scraped magnetic powder is conveyed to the magnetic gap 6 associated with the running of the magnetic tape T and is deposited between the magnetic tape T and the MR-type thin-film magnetic head 3 disposed in the magnetic gap 6. When the magnetic powder is deposited as mentioned above, a so-called spacing loss occurs, thereby leading to a reduced output. As a result, a servo characteristic deteriorates, for example, a servo mechanism becomes unstable, and an error is unlikely detected. This applies also to the magnetic head H1b. 
Especially when the magnetic tape T is stopped and scanned, for example, for playing back a still picture, the magnetic powder of the magnetic tape T is likely scraped.